1. Field of the Invention
The present invention relates to laser systems, and more particularly to optical parametric oscillators for producing relatively high power collimated output beams with low divergence.
2. Description of Related Art
An optical parametric oscillator (OPO) is based on the use of nonlinear optical material within a resonant cavity. As the nonlinear crystal is pumped within the resonator, frequency mixing results in generation of a so called signal beam and a so called idler beam. The pump energy induces gain in both the signal beam and the idler beam, one or both of which can be selected for output using wave length selective elements. Furthermore, the wave lengths of the signal and idler beams can be tuned over a wide range of outputs by adjusting the angular alignment and/or temperature of the non-linear crystal. Thus, the OPO provides one technology for solid state tunable laser systems.
However, high power OPOs tend to operate with larger beam diameters and with large numbers of transverse modes, and are therefore sometimes referred to as highly multimode resonators. Also, high power OPOs using injection seeding suffer interference in the output transverse modes caused by the injection seeding and other parameters of the high power system. For these reasons, highly multimode OPO resonators have not been able to produce a collimated output with low divergence. Thus, for users that require collimated output with low divergence, such as might be used for driving harmonic generators or other similar systems, the highly multimode aspect of OPOs is undesirable.
Accordingly, it is desirable to provide a high power OPO system for producing a low divergence collimated beam overcoming the problems with prior OPO designs.